Visualization of a self-incompatibility gene in Brassica campestris L. by multicolor FISH

The physical localization of the S-glycoprotein (SLG) locus in the chromosome of Brassica campestris L. 'pekinensis' cv 'Kukai' was visualized by multi-color fluorescent in situ hybridization (McFISH). 'Kukai', which is an FI hybrid between two parental lines, T-17 and T-18, has two SLG genes from both T-17 and T-18. In this study, a 1.3-kb DNA fragment was amplified from the genomic DNA of T-17 by PCR using a set of primers specific to the class-I SLG. From the genomic DNA of T-18, no DNA fragment was amplified using these primers. In the genomic Southern hybridization, a cloned PCR product hybridized with the genomic DNA of T-17 or F-1 but not with that of T-18. The PCR product had a sequence homology of approximately, 85% to another class-I SLG gene, SLG-9. Therefore, the PCR product from T-17 was named SLG-17, as it is thought to be a member of the class-I SLG. Using SLG-17 as the probe, FISH was carried out to visualize the position of the SLG locus. McFISH was also carried out simultaneously using the SLG-17 and SLG-9 genes as probes. The SLG-17 gene was detected as a doublet signal at the interstitial region close to the end of a small chromosome, with the signal site being identical to that of SLG-9. Therefore, it is concluded that the SLG-17 gene is localized at the interstitial region close to the end of the chromosome derived from T-17 in Brassica campestris L. 'pekinensis' CV 'Kukai'.